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## Copyright (C) 2004-2013 John Eaton and David Bateman
##
## This file is part of Octave.
##
## Octave is free software; you can redistribute it and/or modify it
## under the terms of the GNU General Public License as published by
## the Free Software Foundation; either version 3 of the License, or (at
## your option) any later version.
##
## Octave is distributed in the hope that it will be useful, but
## WITHOUT ANY WARRANTY; without even the implied warranty of
## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
## General Public License for more details.
##
## You should have received a copy of the GNU General Public License
## along with Octave; see the file COPYING. If not, see
## <http://www.gnu.org/licenses/>.
## -*- texinfo -*-
## @deftypefn {Function File} {@var{y} =} shiftdim (@var{x}, @var{n})
## @deftypefnx {Function File} {[@var{y}, @var{ns}] =} shiftdim (@var{x})
## Shift the dimensions of @var{x} by @var{n}, where @var{n} must be
## an integer scalar. When @var{n} is positive, the dimensions of
## @var{x} are shifted to the left, with the leading dimensions
## circulated to the end. If @var{n} is negative, then the dimensions
## of @var{x} are shifted to the right, with @var{n} leading singleton
## dimensions added.
##
## Called with a single argument, @code{shiftdim}, removes the leading
## singleton dimensions, returning the number of dimensions removed
## in the second output argument @var{ns}.
##
## For example:
##
## @example
## @group
## x = ones (1, 2, 3);
## size (shiftdim (x, -1))
## @result{} [1, 1, 2, 3]
## size (shiftdim (x, 1))
## @result{} [2, 3]
## [b, ns] = shiftdim (x)
## @result{} b = [1, 1, 1; 1, 1, 1]
## @result{} ns = 1
## @end group
## @end example
## @seealso {reshape, permute, ipermute, circshift, squeeze}
## @end deftypefn
function [y, ns] = shiftdim (x, n)
if (nargin < 1 || nargin > 2)
print_usage ();
endif
nd = ndims (x);
orig_dims = size (x);
if (nargin == 1)
## Find the first non-singleton dimension.
(n = find (orig_dims != 1, 1) - 1) || (n = nd);
elseif (! (isscalar (n) && n == fix (n)))
error ("shiftdim: N must be a scalar integer");
endif
if (n >= nd)
n = rem (n, nd);
endif
if (n < 0)
singleton_dims = ones (1, -n);
y = reshape (x, [singleton_dims, orig_dims]);
elseif (n > 0)
## We need permute here instead of reshape to shift values in a
## compatible way.
y = permute (x, [n+1:nd 1:n]);
else
y = x;
endif
ns = n;
endfunction
%!test
%! x = rand (1, 1, 4, 2);
%! [y, ns] = shiftdim (x);
%! assert (size (y), [4 2]);
%! assert (ns, 2);
%! assert (shiftdim (y, -2), x);
%! assert (size (shiftdim (x, 2)), [4 2]);
%!assert (size (shiftdim (rand (0, 1, 2))), [0 1 2])
%% Test input validation
%!error (shiftdim ())
%!error (shiftdim (1,2,3))
%!error (shiftdim (1, ones (2)))
%!error (shiftdim (1, 1.5))
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